For writer and father Po Bronson, yelling praise from the sidelines of a soccer game to his child has always been part of his parental territory. And what parent hasn't done the same, showering gushing platitudes like "You played great" or "You're so smart" at their children at every twist and turn?

But praising your kids, Bronson says now, is what can ruin them. In his latest book, "NurtureShock," written with Ashley Merryman, the science journalist explores some misconceptions about raising children and how certain modern parenting strategies, such as excessively praising children, can do more harm than good.

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Bronson admitted, like others, he's guilty of showering his kids with general praise. Research suggests 85 percent of American parents believe it's important to tell their kids they're smart and to praise them for their intelligence.

"Kids become fixated on maintaining the image of being smart, of never getting anything wrong in front of people, of always looking like they've gotten everything right, of making it look effortless," said Bronson. "Because if you show effort, it's a sign you can't cut it on your natural gifts. And so they make safe choices. They choose classes that won't challenge them. They choose teachers and projects where they know they can get an A."

Bronson said he's trying to reform and all parents should too -- for their the sake of their children.

"The difference is a child who is truly motivated and interested in learning, versus a child who wants to memorize so they can get a good grade so they can keep hearing how smart they are," Bronson explained.

A decade of groundbreaking research suggests that constant praise can lead kids to lose self-confidence, not gain it, and make them actually perform worse, not better.

Bronson relies heavily on the research of Carol Dweck, a professor of psychology at Stanford University.

"I think the self-esteem gurus led us to believe we could hand our children self-esteem on a silver platter through our praise, through our words," said Dweck. "And we thought ... almost the definition of being a good parent was to keep handing the self-esteem to our child. But it doesn't work that way."

'Nightline' Puts Parenting Theory to Test

Over the past decade, Dweck has conducted a series of experiments on 400 fifth-graders from different socio-economic groups across the country. The research provided the basis for one chapter of Bronson's new book and points to a stunning result: Not all praise is created equal. Telling children they're smart can actually hurt them, and you get a far better result if you praise children for challenging themselves, and for effort.

"Nightline" asked Dweck and one of her graduate students to show us how it works.

Mary, 9, and Jameson, 10, were given a series of IQ puzzles and asked to work on them silently. At the end, the researcher gave each child a score. The research assistant praised Mary for being smart, while Jameson was praised for working hard.

After reviewing Mary's answers, the research assistant lauded her: "Wow, you did really well at these problems. You got 8 -- that's a great score. You must be really smart at these problems."

If Dweck's theory holds, Mary will want to continue to look smart, and when given the choice, will opt for a test that shows it -- not something more challenging where they she could learn more.